To evaluate expiratory muscle endurance in middle-aged healthy subjects using incremental as well as constant expiratory loads, 14 healthy volunteers (51 ± 16 years) were submitted to a specific endurance test, which was performed breathing against a threshold valve, and was divided into two parts. In part I, the load was progressively increased (50 g each 2 min) until task failure occurred. The mean mouth pressure generated against the highest load held for at least 60 sec was defined as the maximal expiratory sustainable pressure (Pthmax). In part II, each subject breathed against a constant submaximal expiratory load (80% Pthmax) until task failure occurred (expiratory endurance time or Tth80). Both parts of the test were repeated 24-48 h later. Progressive expiratory loading induced a linear increase in mouth expiratory pressure and the Pthmax obtained was 141 ± 43 cm H2O, representing 74 ± 28% of the maximal expiratory pressure (PEmax). Under constant loads, the Tth80 was 17 ± 9 min. At the end-point of both parts, the tension time index for expiratory muscles was dramatically increased (>0.25), and both EMG central frequency and PEmax were decreased with no changes in maximal inspiratory pressure or inspiratory capacity. Extreme dyspnea was present in most of the subjects but no complications were observed. The endurance of expiratory muscles can be easily assessed in healthy subjects using this method, which has acceptable reproducibility and tolerance.
- Respiratory muscles